Abstract Austrolimnius cleidecostae sp. nov. is one of the smallest species of Elmidae from the Neotropical region. The new species is described and illustrated based on male and female specimens. This species represents the first record in Elmidae of mandibles with an articulated, sclerotized process on inner subapical edge. The specimens were collected from streams in the Atlantic rainforest of São Paulo and Santa Catarina, and habitat notes are given. An updated key for the AustrolimniusCarter & Zeck, 1929 of Brazil is provided. Austrolimnis browniHinton, 1971 and A. musgraveiHinton, 1939 are recorded for the first time from Brazil.

Abstract Heterelmis Sharp, 1882, comprises 22 species and subspecies with 3 species assigned to Brazil so far. Here the forth species, Heterelmis debilis sp. nov. from Brazil, is described and illustrated. The type material is deposited in the Museum of Zoology of the University of São Paulo, São Paulo, Brazil (MZSP) and Natural History Museum, London, UK (NHMUK). Additionally, an identification key with distributional data for Brazilian species is proposed.